This is a proposal to purchase a fluorescence activated cell sorter. Projects initiated by eight investigators will be supported by the proposed instrumentation. Project titles include: Selective Expression of Class 11 MHC Molecules on Human T-Cell Clones (TLC's); Quantitative Variations in Expression of Human MHC Class II Molecules; Phenotypic Characterization of Human T-Lymphocyte Clones; Analysis of Serologic and T-Cell Restriction Epitopes Using Cell Lines Transfected with Hybrid Human MHC Class II Genes; Effects of Platelet Activation in Whole Blood upon Platelet Glycoprotein Receptors: Use of Monoclonal Antibodies and Flow Cytometry; Selection of Specific Antibody-Bearing Peripheral Blood or Splenic 8-Lymphocytes using Antigen, Anti-Idiotypic Antibody or Both; Expression of Analogs of Platelet GPIIb-IIIa on Other Cells; Role of Intracellular Calcium Ions in Platelet Activation; The von Willebrand Proteins and Their Cellular Relationships; The Structure and Functional Similarities of Endothelial Cells and Platelets; Delta Hepatitis and Liver Disease in Hemophiliacs; Significance of Human Platelet Heterogeneity; and Function of Platelet/Endothelial Cell Membrane GP130 as Determined by Analysis of Cell Lines Transfected with GP130 cDNA. The purchase of a fluorescence activated cell sorter will not only support existing projects but will also allow the expansion of research horizons within The Blood Center of Southeastern Wisconsin Research Department. Potential benefits exist for areas of application within immunobiology, platelet biology, coagulation, and immunohematology.